1. NATURAL SELECTION AND ADAPTIVE EVOLUTION
UNIT 5 EVOLUTION

2. Natural Selection A mix of chance and sorting
There is a chance of creating a new genetic variation (mutation)
Natural Selection sorts some alleles over others
The outcome of natural selection is NOT random
It can lead to adaptive evolution

3. Relative Fitness
“Survival of the Fittest” and “Struggle for Existence” often refer to natural selection
Does NOT mean direct competition among individuals
Even though organisms compete for mating privileges, reproductive success is determined by more than just a battle
Relative Fitness – how much an individual contributes to the gene pool of the next generation in comparison to the contributions of other individuals

4. Three Types of Selection
Natural Selection can change the distribution of heritable traits through…
Directional Selection
Disruptive Selection
Stabilizing Selection

5. Directional Selection
Directional Selection – when conditions favor an extreme phenotypic range (shifts in a direction)
Common when environmental conditions or habitats change

6. Disruptive Selection
Disruptive Selection – when conditions favor both extreme phenotypes over the average phenotype (favors both sides)

7. Stabilizing Selection
Stabilizing Selection – when conditions favor average variants but act against extreme phenotypes (shift to the middle)
Reduces the amount of variations in an environment

8. Natural Selection in Adaptive Evolution
Natural Selection increases the frequency of alleles that allow for survival and reproduction
Natural Selection can create an increase in adaptations
But what about genetic drift and gene flow?
Genetic drift – can cause an allele to increase and decrease
Gene flow – can introduce both good and bad alleles
Natural Selection is the only mechanism that can CONSISTENLY lead to adaptive evolution

9. Sexual Selection
Darwin was the first to explore the idea of sexual selection
Sexual Selection – a type of natural selection in which individuals with certain inherited traits are more likely to obtain mates than other individuals
Sexual selection can cause many sexual dimorphisms
Sexual Dimorphisms – differences in secondary sexual characteristics between males and females of the same species
Examples – size, color, behavior, and ornamentation.

10. Types of Sexual Selections
Intrasexual Selection
Intersexual Selection

11. Intrasexual Selection
Intrasexual Selection – sexual selection within the same sex
Occurs when individuals of one sex compete with the same sex for individuals of the opposite sex
Can occur in both men and women

12. Intersexual Selection
Intersexual Selection – when members of one gender make mating choices based off specific characteristics of the opposite gender
“Mate Choice”
Female often choose based on male’s behavior or appearance